Better error reporting

src/bin/generate.ts

@@ -110,6 +110,26 @@ async function main() {
 }
 
 main().catch(error => {
+  if (typeof error === 'string') {
+    github.setOutput('error', error);
+  } else if ('message' in error && typeof error.message === 'string') {
+    if ('stack' in error && typeof error.stack === 'string') {
+      if (error.stack.includes(error.message)) {
+        github.setOutput('error', error.stack);
+      } else {
+        github.setOutput('error', error.message + '\n' + error.stack);
+      }
+    } else {
+      github.setOutput('error', error.message);
+    }
+  } else {
+    try {
+      github.setOutput('error', JSON.stringify(error));
+    } catch {
+      // ignore
+    }
+  }
+
   console.error(error);
   process.exit(1);
 });

src/lib/walker.ts

@@ -1,41 +1,115 @@
-import { Root } from 'mdast';
+import { Heading, Root } from 'mdast';
+import markdown from 'remark-parse';
+import stringify from 'remark-stringify';
 import { Option, assert } from 'ts-std';
+import unified from 'unified';
 import { Node, Parent } from 'unist';
 import { VFile } from 'vfile';
 
+
 type Handler<Options> = (this: Walker<Options>, node: Node) => Option<Node> | Promise<Option<Node>>;
 
 function isParent(node: Node): node is Parent {
   return Array.isArray(node.children);
 }
 
+const Printer = unified().use(markdown).use(stringify);
+
 export default class Walker<Options> {
+  private lastNode: Option<Node> = null;
+  private lastHeading: Option<Heading> = null;
+
   constructor(protected options: Options, protected file: VFile) {}
 
   [key: string]: unknown;
 
   async walk(root: Node): Promise<Root> {
     assert(root.type === 'root', `Cannot walk \`${root.type}\` (must be \`root\`)`);
 
-    let result = await this.handle(root);
+    try {
+      this.lastNode = null;
+      this.lastHeading = null;
 
-    if (Array.isArray(result)) {
-      assert(result.length === 1, 'Must return a single root node');
-      result = result[0];
-    }
+      let result = await this.handle(root);
 
-    if (result) {
-      assert(result.type === 'root', 'Must return a root');
-      return result as Root;
-    } else {
-      return {
-        type: 'root',
-        children: []
-      };
+      if (Array.isArray(result)) {
+        assert(result.length === 1, 'Must return a single root node');
+        result = result[0];
+      }
+
+      if (result) {
+        assert(result.type === 'root', 'Must return a root');
+        return result as Root;
+      } else {
+        return {
+          type: 'root',
+          children: []
+        };
+      }
+    } catch (error) {
+      let message: string = 'Encounted an error';
+
+      if (this.file.path) {
+        message += ` while processing ${this.file.path}`;
+      }
+
+      if (this.lastNode?.position) {
+        let { line, column } = this.lastNode.position.start;
+        message += ` at L${line}:C${column}`;
+      }
+
+      if (this.lastHeading) {
+        try {
+          let heading = Printer.stringify(this.lastHeading);
+          message += ` (under the section "${heading}")`;
+        } catch {
+          // ignore
+        }
+      }
+
+      if (typeof error === 'string') {
+        message += `.\nReason:\n${error}`;
+      } else if ('message' in error && typeof error.message === 'string') {
+        if ('stack' in error && typeof error.stack === 'string') {
+          if (error.stack.includes(error.message)) {
+            message += `.\nReason:\n${error.stack}`;
+          } else {
+            message += `.\nReason:\n${error.message}\n${error.stack}`;
+          }
+        } else {
+          message += `.\nReason:\n${error.message}`;
+        }
+      }
+
+      let reason: Error | string;
+
+      if ('stack' in error && typeof error.stack === 'string') {
+        reason = new Error(message);
+
+        if (error.stack.includes(error.message)) {
+          reason.stack = error.stack.replace(error.message, message);
+        } else {
+          reason.stack = error.stack;
+        }
+      } else {
+        reason = message;
+      }
+
+      // upstream type for reason is wrong: should be Error | string
+      this.file.fail(reason as string, this.lastNode?.position);
+    } finally {
+      this.lastNode = null;
+      this.lastHeading = null;
     }
   }
 
   protected async handle(node: Node): Promise<Option<Node> | Node[]> {
+    this.lastNode = node;
+
+    if (node.type === 'heading') {
+      this.lastHeading = node as Heading;
+    }
+
     let maybeHandler = this[node.type];
 
     if (typeof maybeHandler === 'function') {